1. Field of the Invention
The present invention relates to the heating-up and degassing of water by means of steam in a power station plant. It relates to a corresponding apparatus as described in the preamble of the first claim.
2. Discussion of Background
In modern power station plants the consumption of make-up water is very high. Thus conventional power station plants already normally require as make-up water 1 to 5% of the entire circulating mass flow of the steam/condensate circuit. In combined-cycle plants, however, in which the emission of nitrous oxides is reduced by means of steam injection, this consumption of make-up water may rise to more than 50%. In this case, as a result of today's requirements, a degassing range of the make-up water with respect to O.sub.2 from 8000 ppb (parts per billion) i.e. saturation state of the water with the atmospheric air at room temperature--down to about 5 ppb with simultaneous heating of around 20K and above is required.
The simple, direct injection of make-up water into the condenser, which injection is known per se and is conventional practice in the case of small quantities of make-up water from 1 to 5%, would lead to flooding of the tube banks on account of said large quantities. This would result in severe impairment of the function of the condenser and is therefore approved by neither the condenser supplier nor the condenser operator. In addition, the desired heating-up and degassing cannot be achieved in this way. Above a quantity of make-up water of about 5% of the total mass flow, conventional apparatuses are used for the heating-up and degassing, these apparatuses being arranged separately from the condenser and, depending on their construction, being supplied with exhaust steam or higher-grade steam for the heating-up and degassing via corresponding lines. However, the use of such apparatuses is only appropriate above a requirement for make-up water of more than 30% of the total mass flow. At a requirement for make-up water of between 5 and 30%, the cost of a separate degasser calls the use of the same into question.
EP 0 463 448 B2, for example, discloses a known apparatus for the heating-up and degassing of make-up water in large quantities.